by Carl Strang
The Mesozoic Era came to an abrupt end with the arrival of an asteroid, about 6 miles in diameter, that slammed into the Earth in the vicinity of the present-day Yucatan Peninsula. The details and ramifications of that and similar events continue to attract the attention of researchers, as today’s notes from last year’s literature show.
Robertson, Douglas S., William M. Lewis, Peter M. Sheehan, Owen B. Toon. 2013. K-Pg extinction: Reevaluation of the heat-fire hypothesis. Journal of Geophysical Research: Biogeosciences, DOI: 10.1002/jgrg.20018 From a ScienceDaily article. This modeling study suggests that when the end-Mesozoic asteroid struck, it pulverized and spread a huge volume of rock material. This overheated dust spread worldwide through the atmosphere, heating the planet’s surface for a few hours to the point of setting off fires that could have killed nearly all animals and plants on or above the surface of the ground and water.
Renne, P. R., et al. 2013. Time scales of critical events around the Cretaceous-Paleogene boundary. Science 339: 684-687. Dating is becoming more precise, and this study places the Chicxulub impact event at 66,043,000 years ago, within error at precisely the time non-avian dinosaurs went extinct (the KPB, or Cretaceous-Paleogene Boundary). The authors point out, however, that stresses of climate change probably caused by the Deccan Traps volcanic eruptions had stressed the Earth’s life forms to the point where this more readily tipped the scale to mass extinction. Those massive basalt lava flows occurred within a million years prior to the Chicxulub impact, but the dating there is less precise. There were “six abrupt shifts of >2°C in continental mean annual temperatures…The most dramatic of these temperature oscillations, a drop of 6° to 8°C, occurred <100 ky [thousand years] before the KPB and was closely synchronous with notable mammalian turnover…” All these results are from studies in Montana. Sea levels also are believed to have fluctuated drastically during this time, so that brief periods of glaciation may have occurred. In Montana and adjacent Canada, mammalian faunas changed at the KPB, but that change is believed to be the result of immigration rather than the evolution of new species given the brief time interval involved.
Sanford, Ward E., et al. 2013. Evidence for high salinity of Early Cretaceous sea water from the Chesapeake Bay crater. Nature 503 (7475): 252 DOI: 10.1038/nature12714 As described in a ScienceDaily article. Chesapeake Bay was created around the Eocene-Oligocene boundary, 35 million years ago, by an impact of comet or asteroid. The result was the Bay’s 56-mile-wide basin and a disruption of aquifers, one of which is found to preserve a body of Cretaceous seawater, a kilometer below the bay’s floor. The Eocene ended with a mass extinction, but the article does not mention this.